Energy storage devices, including batteries and capacitors, are used extensively in electronic devices. In particular, capacitors are widely used for applications ranging from electrical circuitry and power delivery to voltage regulation and battery replacement. As capacitor technology has continued to develop, several types have emerged. For example, electric double-layer capacitors (EDLCs), also referred to as ultracapacitors (among other names), are characterized by high energy storage and power density, small size, and low weight and have thus become promising candidates for use in several applications. The total energy that an electrochemical capacitive device can store is often determined by the useful surface area of the device, the spacing between the accumulated charges, the permittivity of the intervening dielectric material, and the square of the voltage of the device. Conventional electrochemical capacitors are limited in their voltage range to just a few volts depending on the electrolyte and electrode used.
Conventional capacitors currently are formed using thicker dielectrics to prevent electrical breakdown and leakage at a high cost to the overall capacitance. Electrolytic capacitors in common use are prepared electrolytically using either aluminum or tantalum. This process is not easily transferable to high specific surface area electrodes. Tantalum capacitors have generally better performance, but at a higher price. Additionally, most electrolytic capacitor technology is focused on ultra-high voltage applications requiring very thick (thousands of nm) dielectric layers.
For simplicity and clarity of illustration, the drawing figures illustrate the general manner of construction, and descriptions and details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the discussion of the described embodiments of the invention. Additionally, elements in the drawing figures are not necessarily drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of embodiments of the present invention. The same reference numerals in different figures denote the same elements, while similar reference numerals may, but do not necessarily, denote similar elements.